In recent years, solar power has become increasingly examined and used as a viable alternative to current energy production systems. There are many different methods and apparatuses for producing power from solar energy, but a more common and viable method includes systems which use reflective surfaces to concentrate or focus sunlight onto a receiving location where it is converted to electrical or thermal energy. However, to maximize the transfer and concentration of solar energy and increase energy production efficiency, the reflective surfaces must be precisely aligned to the receiving location.
Of these solar concentrating devices utilizing reflective surfaces, one of the more useable approaches includes dish concentrators having paraboloidal reflecting surfaces which reflect the solar or other energy to a receiver or receiving location. Typically, the paraboloidal surfaces are made up of individual reflective surfaces of facets which direct the impinging energy such that the maximum concentration of solar flux is focused at the collector or receiver. To maximize the efficiency of the concentrator, as well as increase usability in differing environments, each facet surface is individually adjustable.
Each reflective surface or facet must be individually adjusted such that it is precisely aligned to reflect the optimum concentration of solar power or flux to the receiver. In general, the receiver is located at the focal point of the concentrator. In addition, each facet is preferably aligned such that the flux reflected from each facet strikes the receiver at a slightly different locations or points. Thus, each facet will generally have a slightly different aimpoint.
In particular, the flux distribution on the receiver must be distributed so as to prevent hot spots of excessive flux concentration. This distribution increases the efficiency of the concentrator and extends the life of the receiver. Thus, there is a need for an apparatus and method for precisely aligning individual facets on a dish concentrator. This need for precise alignment also applies to dish concentrators and antennas used in radar, electromagnetic and other energy applications.
In order to align each facet so that the amount of flux at the aim point, or within a given distance of the aim point, is maximized to a high statistical confidence level, a large amount of data relating to the reflecting facets must be obtained. The data is generally taken from spaced apart locations on each facet and then used to calculate the best estimate of the facet normal. Once the facet normal is determined, the facet can be precisely aligned relative to that normal. Thus, there is a need for an apparatus and method that can obtain and utilize a large amount of data from each facet.
Quantitatively measuring actual alignment accuracy for each facet provides information that can be used to determine the performance of the concentrator. This alignment accuracy data can also be archived and used to identify future performance problems such as whether the alignment of any facet has changed. Thus, there is a need for an apparatus and method that can determine facet alignment accuracy and system performance as well as archive such data.
A method and system for determining the surface characteristics of objects is described in U.S. Pat. No. 5,477,332. More specifically, this patent discloses a method and apparatus using digital imaging radiometer technology to determine the optical characteristics of a reflective or refractive surface such as a concentrator facet. However, the system cannot determine the inertia position of each facet normal on a dish concentrator and cannot provide alignment information.
A prior art method for aligning facets on a dish concentrator uses a beam of light and a target or screen mounted on the concentrator. The light is reflected from each of the facets and onto the target or screen. An optical computer is used to calculate the projections of the facet corners onto the screen. The angular position of the facets is then adjusted until the light image is within defined boundaries. Although this system provides the ability to align individual facets, precise alignment accuracy is not possible.
For example, the system relies on human judgement as to when the light image on the screen is in the best location with respect to the calculated image. Since judgements differ, each person generally adjusts each facet slightly differently. Additionally, the process requires close attention and is tiring, leading to a loss of alignment accuracy as well as mistakes as the person doing the aligning becomes fatigued. Thus, there is a need for a system that does not rely on human judgement.
An additional problem with this prior art system occurs when aligning the facets at different aim points on the receiver or correcting for the effects of gravity bending on the concentrator. In these situations, the theoretical projected light images of some of the different facets will overlap. In order to align a facet, neighboring facets with overlapping light images must be covered up. This covering and uncovering of facets greatly increase the time, labor and costs to perform the alignment process.
In order to distinctly see the reflective light images the process must be done in the dark. For an installed dish concentrator, this means the alignment process would have to be conducted at night. Moonlight is an additional problem. Thus, there is a need for an apparatus and method for precisely aligning individual facets on dish concentrators that is relatively simple and does not require darkness.
An additional problem encountered with dish concentrators occurs during field set-up or when a facet on an active concentrator is damaged or otherwise needs to be repaired and realigned. The problem is worsened when the concentrator is in a remote or otherwise inaccessible location. To accommodate these repairs, the alignment system must be portable such that it can be easily transported to the location of the concentrator. The system must also be easily set-up and quickly operational in order to reduce the downtime of the damaged concentrator. Thus, there is a need for a facet alignment system that can be used with a commercial concentrator system that is cost effective, fast and requires little attention from high-skilled personnel. Additionally, there is a need for a light-weight and very portable alignment system that can be easily transported into remote areas, including space applications.